POJ 3126 Prime Path (BFS + 素数筛)

/*************************************************************************
	> File Name: E.cpp
	> Author: 
	> Mail: 
	> Created Time: 2017年11月26日 星期日 10时51分05秒
 ************************************************************************/

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <queue>
using namespace std;

#define MAX_N 100000
int isPrime[MAX_N] = {0}, primeList[MAX_N] = {0};
int T;
int vis[MAX_N];
struct info {
    info() {}
    info(int num, int step) : num(num), step(step) {}
    int num, step;
};
info st, ed;

void init_prime() {
    for (int i = 2 ; i < MAX_N ; ++i) {
        if (!isPrime[i]) {
            primeList[++primeList[0]] = i;
        }
        for (int j = 1 ; j <= primeList[0] ; ++j) {
            if (i * primeList[j] >= MAX_N) break;
            isPrime[i * primeList[j]] = 1;
            if (i % primeList[j] == 0) break;
        }
    }
}

// 在num的第i个位置上替换为j
int transInfo(int i, int j, int num) {
    int temp[4], k = 3, ret;
    while (num) {
        temp[k--] = num % 10;
        num /= 10;
    }
    temp[i] = j;
    return temp[0] * 1000 + temp[1] * 100 + temp[2] * 10 + temp[3];
}

int check(info p) {
    if (p.num < 1000 || p.num >= 10000) return 0;
    if (vis[p.num]) return 0;
    if (isPrime[p.num]) return 0;
    return 1;
}

int BFS() {
    queue<info> que;
    vis[st.num] = 1;
    que.push(st);
    while (!que.empty()) {
        info now = que.front();
        que.pop();
        if (now.num == ed.num) {
            return now.step;
        }
        for (int i = 0 ; i < 4 ; ++i) {
            for (int j = 0 ; j < 10 ; ++j) {
                // 最高位不能为0
                if (i == 0 && j == 0) continue;
                info temp(transInfo(i, j, now.num), now.step + 1);
                if (!check(temp)) continue;
                vis[temp.num] = 1;
                que.push(temp);
            }
        }
    }
    return 0;
}
void solve() {
    memset(vis, 0, sizeof(vis));
    st.step = 0;
    int ret = BFS();
    printf("%d\n", ret);
}

int main() {
    // freopen("./in.in", "r", stdin);
    init_prime();
    scanf("%d", &T);
    while (T--) {
        scanf("%d%d", &st.num, &ed.num);
        solve();
    }
    return 0;
}